XUV + IR ionization of Argon atoms

GRAMAJO, A. A.; R. DELLA PICCA; LÓPEZ, S. D.; ARBÓ, D. G.

budapest

Conferencia; The International Conference on Many Particle Spectroscopy of Atoms, Molecules, Clusters and Surfaces; 2018

The laser-assisted XUV photoelectric effect (LAPE) occurs when extreme ultraviolet (XUV) and infrared (IR) lasers overlap in space and time. In this case, the photoelectron spectrum is factored into two contributions: one that accounts for the intracycle (during one IR cycle time interval) electron emission and the second one describing the intercycle interference (due to the emission at different IR cycles) [1,2,3]. This intercycle interference is the responsible of the well-know ?sidebands? (Sbs) in the photoelectron spectrum separated at energy values given byEn = nωL + ωX - Ip - Up (1) where ωX(L) is the frecuency of XUV(IR) pulse, Ip is the ionization energy, Up the ponderomotive energy and n is the number of absorbed or emitted IR photons.In the present work we consider the Argon photoionization from the subshells 3s, 3p0 and 3p1 due to a short XUV pulse assisted by an IR laser both linearly polarized. Within the continuum-distorted wave Strong Field Approximation (SFA) supported by the ab initio solution of the time-dependent Schrödinger equation (TDSE) we study the angle-resolved momentum distribution of photoelectron for the case that both fields are linearly polarized. We analyze and characterize the modulation of both factors, the intra- and intercycle contributions, on the spectrum.In particular, we study several geometrical arrangements between the polarization vectors and the emission direction, that give rise to selective photoelectron sideband energies in the the ionization spectrum, as in the case of perpendicular emission where only odd sidebands are observed (see figure (b) and [3]). In the figure, we show the SFA momentum distribution of the emitted electrons from 3s (a), 3p0 (d) and 3p1 (e) subshells of hydrogen-like Argon atoms for the case where both lasers are linearly polarized in the same direction. In figures (b) and (c) we particularize the spectra for perpendicular and forward emission cases. It can be observed that in the first case the even sideband orders are selectively canceled whereas in the forward emission all sidebands are present.During the conference we will theoretically analyze the selection rules that governs the allowed photoelectron energies, showing that the intra-half-cycle factor [1,3] destructively interfere to cancel some sidebands peaks. Figure 1. SFA photoelectron momentum distribution for LAPE process of Argon atoms in arbitrary units, (a) from the 3s, (d) 3p0 and (e) 3p1 intital states. Differential emission probability in (b) perpendicular and (c) forward emission. The IR and XUV laser parameters are ωL = 0.057, FL0 =0.041, FX0 = 0.01 and ωX = 2.3 (all in atomic units). The XUV pulse duration is 3 IR cycles. In (b), TDSE calculation in black line. This work has been supported by ANPCyT (Argentina PICT-2016-0296 y 2016-3029).References[1] A A Gramajo et al, J. Phys. B: At. Mol. Opt. Phys. 51, 055603 (2018).[2] A A Gramajo et al, Phys. Rev. A 94, 053404 (2016).[3] A A Gramajo et al, Phys. Rev. A 96, 023414 (2017).